Process for monitoring a moving yarn sheet and apparatus for the execution of this process

Abstract

Process for monitoring a moving yarn sheet by means of a light beam, photodetectors and an electronic analyzer, whereby the yarn sheet is guided via thread guide rods before and after the monitoring site and the shadowing of the light beam caused by an increase in thread thickness is directed perpendicularly to the direction of travel of the yarn sheet for detection by photodetectors, and evaluated and recorded by the electronic analyzer, characterized in that the intensity of a single light beam is detected by at least two photodetectors arranged in series in the direction of travel of the yarn sheet and in that the evaluation by the electronic analyzer is such that a recording only takes place when the shadowing is detected by one or more of said photodetectors following in the direction of travel of the yarn sheet with a time delay corresponding to the running speed of the yarn sheet is disclosed. It is preferred to employ at least four photodetectors of which at least two are situated in series in the direction of travel of the yarn sheet and at least two are arranged one above the other such that at least one photodetector is positioned below the yarn sheet plane and at least one photodetector is positioned above the yarn sheet plane.

What is claimed is: 
     
       1. A process for monitoring a moving yarn sheet comprising guiding said yarn sheet via thread guide rods before and after a monitoring site, emitting a single light beam perpendicularly to the direction of travel of said yarn sheet and parallel to the yarn sheet plane to photodetectors, evaluating and recording the signals of said photodetectors by an electronic analyzer, detecting the intensity of said single light beam by at least two of said photodetectors arranged in series in the direction of travel of said yarn sheet, carrying out the evaluation by said electronic analyzer such that a recording only takes place when the shadow projected upon one or more photodetectors which are sequentially arranged in the direction of travel of said yarn sheet is detected as having a time delay corresponding to the running speed of said yarn sheet, widening said light beam to a maximal 30 mm before striking said yarn sheet and focusing the width of said light beam beyond said yarn sheet such that it illuminates all photodetectors assigned to it. 
     
     
       2. The process in accordance with claim 1, wherein the said light beam is widened up to a maximal 10 mm and then sent through the yarn sheet and that said light beam is focused beyond said yarn sheet such that it covers at least the entire surface area of all photodetectors assigned to it. 
     
     
       3. The process according to claim 1, wherein two photodetectors are employed, said two photodectors being contained in one double photodetector. 
     
     
       4. The process according to claim 1, wherein two photodetectors in series are employed, the amplified signals from each of said two photodetectors in series struck by a single light beam are directed to a differential amplifier and in that the electronic analyzer only transmits a signal for recording when the differential signal exceeds a predetermined level. 
     
     
       5. A process for monitoring a moving yarn sheet, wherein the process is, according to claim 1, repeated in the direction of travel of said yarn sheet. 
     
     
       6. A process for monitoring a moving yarn sheet comprising guiding said yarn sheet by means of thread guide rods before and after a monitoring site, emitting at least one light beam perpendicularly to the direction of travel of said yarn sheet and parallel to the yarn sheet plane to photodetectors evaluating and recording the signals of said photodetectors by means of an electronic analyzer, employing one or more light beams and at least four photodetectors for monitoring, of which at least two are positioned in series in the direction of travel of the yarn sheet and at least two are positioned one above the other such that at least one photodetector is situated below and one photodetector is situated above the yarn sheet plane. 
     
     
       7. The process according to claim 6, wherein 50% of all photodetectors are arranged above the yarn sheet plane and 50% of all photodetectors are positioned below it. 
     
     
       8. The process according to claim 6, wherein each upper photodetector is arranged adjacent to one lower photodetector. 
     
     
       9. A process according to claim 8, wherein the electronic analyzer detects a lint signal I, formed by adding up the signals emitted by the photodetectors arranged one above another and by subtracting the sums detected by two photodetector pairs in series and determines a thread jump signal II, which is formed by adding up the signals emitted by two photodetectors arranged in series and by the difference of the sums detected by two photodetector pairs arranged one above the other, and in that a lint is recorded when the attenuated thread jump signal II is subtracted from lint signal I and the difference exceeds a predetermined lower threshold value. 
     
     
       10. The process according to claim 9, wherein said electronic analyzer emits a stop signal VI if the lint signal I exceeds a predetermined upper threshold value and at the same time a lint has been recorded. 
     
     
       11. The process according to claim 9, wherein the electronic analyzer determines the size of the lint by the strength of the lint signal (I) when a lint is recorded. 
     
     
       12. The process according to claim 6, wherein photodetectors which are arranged in series are adjacent. 
     
     
       13. The process according to claim 6, wherein all photodetectors are illuminated by a single light beam. 
     
     
       14. The process according to claim 13, wherein the light beam is widened before striking the yarn sheet. 
     
     
       15. The process according to claim 14, wherein the light beam is widened up to a maximal 30 mm and that the width of the light beam is focused beyond the yarn sheet such that it illuminates all photodetectors assigned to it. 
     
     
       16. The process according to claim 15, wherein the light beam is sent through the yarn sheet with a width not exceeding 10 mm and is focused beyond the yarn sheet to a width not exceeding 6 mm. 
     
     
       17. The process according to claim 6, wherein the process is carried out using double photodetectors. 
     
     
       18. The process according to claim 6, wherein the process is carried out using a four-quadrant photodetector. 
     
     
       19. The process according to claim 6, wherein the process is carried out using a multisegment photodetector. 
     
     
       20. An apparatus for monitoring a moving yarn sheet according to claim 6 with at least one light source and photodetectors, wherein the apparatus possesses at least four photodetectors, of which at least two photodetectors are positioned in series in the direction of travel of the yarn sheet and at least two photodetectors are arranged one above the other. 
     
     
       21. The apparatus according to claim 20, wherein all photodetectors are arranged such that respective pairs are formed one above the other and all pairs are arranged in series. 
     
     
       22. The apparatus according to claim 20, wherein 50% of all photodetectors are positioned above a yarn sheet plane and 50% of all photodetectors are positioned below it. 
     
     
       23. An apparatus according to claim 20, wherein the light beam consists of collimated light. 
     
     
       24. An apparatus according to claim 20, wherein the light beam is a laser beam.